Private automatic telephone exchanges employing nonnumerical switches for interconnecting local lines, and for interconnecting local lines and trunk lines



Get. 25, 1949. JJ'H, voss 2,486,231

PRIVATE AUTOMATIC mmruonm ,Excmuess EMPLOYING v nounmmnzcm. SWITCHES FOB INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECTI'NG LOCAL LINE S AND flRUNK LINES 8 Sheets-$het 1 Filed June 29, 1945 nnv== J Iut mmzq ON ZOFaFm IQCEmMZI .m ZOFEb om zorzhm JOHN H. voss" ATTORNEY 8 Sheets-Sheet 2 J. H. VOSS LOCAL LINES AND TRUNK LINES NONNUMERICAL SWITCHES FOR INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECTING PRIVATE AUTOMATIC TELEPHONE EXCHANGES EMPLOYIEG Oct. 25, 1949.

Filed June 29, 1945 mnm SN INVENTOR. JOHN H. voss BY r ATTORNEY NwN Oct. 25, 1949. v J. H. voss 2,486,231

PRIVATE AUTOMATIC TELEPHONE EXCHANGES EMPLOYING NONNUMERICAL SWITCHES FOR INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECTING LOCAL LINES AND TRUNK LINES June 29, 1945 8 Shoe mms os a L-mxsl a a 3 PART 0 F L INKI mm INVENTOR. 4 JOHN H. voss ATTORNEY Oct; 25,v 1949. J. H. voss 2,486,231

PRIVATE AUTOMATIC TELEPHONE EXCHANGES. EMPLOYING NONNUMERICAL SWITCHES FOR INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECTING LOCAL LINES AND TRUNK LINES A INVENTOR. JOHN H .VOSS

ATTORNEY J. H.- v'oss Oct. 25, 1949.

PRIVATE AUTOMATIC TELEPHONE EXCHANGES EMPLOYING NONNUMERICAL SWITCHES FOR INTERcoNNEcTING LOCAL LINES, AND FOR INTERCONNECTING LOCAL LINES AND TRUNK LINES Filed June 29, 1945 8 Sheets-Sheet 5 IO CO N an m mm m ow mm 7 m 8m 33 B 1.; I v? 0mm &mm :mm

mm mm mm mm 5 S Em 5% 4535 EKEM INVENTOR. JOHN H. VOSS ATTORNEY mm mmm .N 3 NS o zoEFw J. H. VOSS Oct. 25, 1949. PRIVATE AUTOMATIC TELEPHONE EXCHANGES EMPLOYING NONNUMER'ICAL SWITCHES FOR INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECTING LOCAL LINES AND TRUNK LINES 8 Sheets-Sheet 6 Filed 'June 29. 1945 w 51mm mm F2 Qwm J Nmm L n INVENTOI.

JOHN H. VOSS [ATTORNEY J. H.V PRIVATE AUTOMATIC TELEPHONE EXCHANGES EMPLOYING NONNUMERICAL SWITCHES FOR INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECTING LOCAL LINES AND TRUNK LINES Oct. 25, 1949. 2,486,231

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" f a 2' ,2 9 d |L Ll. Llx 1% 8 INGOMING CALL SIGNAL DISTANT INVENTOR. JOHN H. voss ATTORNEY PRIVATE AUTOMATIC TELEPHONE EXCHANGES EMPLOYING NONNUMERICAL SWITCHES FOR INTERCONNEGTING LOCAL LINES, AND FOR INTERCONNECTING LOCAL LINES AND TRUNK LINES Oct. 25, 1949. I J. H. voss 2,486,231

Filed June 29, 1945 8 Sheets-Sheet 8 Q :g m & m 2* cm N In x x x Z Z Z 3 3 3 m o v a N J '0 l J v J J 2' 6 o \8- s01 n JgJ co m m on O m .1- m

Q 2 0 LL 54 m o O u. n is '83 2 INVENTOR. JO HN H VOSS AT TO B EY Patented Oct. 25, 1949 PRIVATE AUTOMATIC TELEPHONE EX- CHANGES EMPLOYIN G N ONNUMERICAL SWITCHES FOR.

INTERCONNECTING LOCAL LINES, AND FOR INTERCONNECT- ING LOCAL LINES AND TRUNK LINES John H. Voss, Downers Grove, 11]., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 29, 1945, Serial No. 602,231

27 Claims. 1

The present invention relates in. general to telephone systems, and more Particularly to systems of the type commonly known as private auto matic telephone exchanges.

Private automatic telephone exchanges are installed in business and other establishments for providing local service between a relatively small number of local telephone stations, and for completing connections between the local telephone stations and another telephone exchange over trunk lines.

An object of the invention is to provide an economically arranged private automatic telephone exchange wherein the minimum amount o-ii switching equipment is required to enable a local telephone station to. connect with a particular trunk line extending to another telephone exchange, and which can be. manufactured very inexpensively, without sacrificing the desirable, service facilities usually provided in more. costly types of private exchanges.

Another object of the. invention is to provide a new and novel arrangement whereby interconnections between the local telephone stations in the local automatic exchange, and interconnections between local telephone stations and trunklines leading to a distant exchange, are completed by means of non-numerical switches under the control of the. local telephone stations A further object of the invention is to provide in the local automatic exchange novel arrangements whereby certain local telephone stations are permitted to call through to a distant exchange over the trunk lines interconnecting the two exchanges, and other local telephone stations are automatically barred from connecting with the trunk lines when they attempt to make outgoing trunk calls. to the. distant exchange.

A still further object of the invention is to provide in the local automatic exchange. special service facilities. additional to the facilities ordinarily provided for the handling of trunk connections. between the local exchange and the distant exchange These additional facilities include novel means for enabling certain of the local telephone stations to. connect automatically with a previous ly established trunk-line connection Whenever such local telephone stations, initiate a call for the particular engaged trunk-line, means for completin outgoing trunk calls for the local telephone stations normally barred from making such calls directly over the trunk lines, and means for establishing a conference circuit connection between any trunk line and two or more local telephone stations.

Another object oi the invention, is to provide new and novel circuit means in an automatic telephone exchange. of th foregoing character for accomplishing the various telephone connec tions in a simple and efficient manner. I

A feature of the invention is tht provision of an improved call allotter which controls the extension of marking designations to a single mastension of the marking designations to the master switch that one local station non-numerical switch is effective at a time and, therefore, there can be no false local link or trunk-line. assignments due to. simultaneous calls for connections.

Another feature of this invention. resides in the circuit arrangement whereby a calling local telephone station is given a, distinctive signal; when actuating the connect key associated with a previously engaged trunk line for indicating to the calling telephone station that the particular trunk line is in prior use. The calling local telephone station thereupon actuates the connect key as.- sociated with another trunk line and, assumin that. this latter trunk line is free, the actuation of the second trunk connect key causes the connection of the calling telephone station with the idle trunk line.

A further feature of the invention is the provision in each trunk line of a novel self-locking holding circuit which does not guard the trunk line from another calling local telephone station after the calling local station'which set up the holding condition in the particular trunk line releases from the held trunk line. Hence, a local telephone station normally barred from directly connecting with a trunk line for the purpose of making an outgoing trunk call to the distant exchange, can connect with a, held trunk line and complete an outgoing call to the distant exchange.

A still further feature, of the invention relates to the reduction of switching equipment. Each trunk line from the distant exchange is directly accessible to the non-numerical switches of the local telephone stations, and. connections between the trunk lines and the local telephone stations are completed without using the local interconnecting links in any manner.

Another feature of the invention is. the accessing of each two-way trunk line from the local telephone stations by means of three separate control leads, each control lead terminating at a different point in the trunk line, thereby providing facilities so that certain local telephone stations. can connect with any trunk line on both incoming calls from and outgoing calls to the distant exchange, other local telephone stations can connect with the trunk lines only when answering incoming trunk calls, and still other local telephone stations can connect with the trunk lines on both incoming and outgoing trunk calls even though the selected trunk line is in prior use.

There are other objects and features of the invention having to do for the most part with the circuit details necessary to carry out the objects and features above mentioned.

The various objects and features of the invention will be understood best from a perusal of the following detail description of the drawings comprising Figs. 1 to 8 inclusive, which show by means of the usual circuit diagrams a sufficient amount of apparatus to enable the invention to be described and understood.

Fig. 1 illustrates, at the left-hand edge, two local station telephone instruments each equipped with a series of interlocking push buttons by means of which a person at the associated station telephone can make and receive local calls, make and receive trunk calls, and hold a trunk call. Two lineswitch circuits, one for station #2! and one for station #20, are shown at the center of Fig. l. The wipers and banks associated with the two line switches are shown at the right of Fig. 1, together with the multiple connections to other lines switch banks.

Fig. 2 shows, in the upper portion, the units and tens relays associated with the local stations for permitting one call at a time to be registered for extension to a local interconnecting link or to a distant-exchange trunk circuit. In the lower portion of Fig. l are shown the relays which pre-assign a free local interconnecting link.

Fig. 3 shows the portions of local interconnecting links #I, #2 and #3 which co-operate with the relays of Fig. 2 for connecting local stations to the local interconnecting links.

Fig. 4 shows in its lower left-hand corner a master switch for aligning the plungers of the station line switches with the proper contacts of the banks connected to the local interconnecting links and to the distant-exchange trunk circuits. The balance of Fig. 4 shows most of the relays and circuit of local interconnecting link #I.

Fig. 5 shows in its upper right-hand corner the telephone instrument and associated interlocking keys for local station #310. At the upper center, is shown the lineswitch. circuit associated with local station #30 and, at the upper left, the wipers and banks of line switch #30 together with the multiple connections to other lineswitch banks In the lower portion of Fig. 5 are shown two switching relays associated local interconnecting link #I.

Fig. 6 shows the register relays for registering the digits dialled by a calling local station when making a call to another local station.

Fig. '7 shows, in the upper portion, the relays and circuit of distant-exchange trunk #I. In the lower portion of Fig. 7 is a plan illustrating the order in which the drawings may be assembled to form a continuous circuit diagram.

Fig. 8 illustrates in simple diagrammatic form the association of three local interconnecting links and four distant-exchange trunk lines with the banks of the local-station lineswitches.

The telephone system disclosed in Figs. 1 to 7 inclusive is an automatic telephone system wherein all the local telephone stations may connect with each other and may answer incoming calls from a distant exchange, other local telephone stations may also make outgoing calls to the distant exchange, and certain local telephone stations enjoy all of these services and, in addition, may connect with a previously engaged trunk line.

Referring now to Fig. 1, all local stations, such as stations #20 and #2l, are each equipped with a standard well-known automatic telephone in strument comprisin a cradle-type receiver and transmitter handset piece, a cradle switch and associated contact springs, an induction coil, and a ringer. Since the arrangements of these components and the interwiring of same are well known, no detail circuit diagrams of the instruments are included in Fig. 1, the instruments at stations #20 and #2I being represented by squares l0 and H0 respectively. Associated with each telephone instrument is a set of key switches mechanically interlocked with each other and with the cradle switch in a manner similar to that disclosed in Patent No. 1,783,310 dated December 2, 1930. Each station telephone instrument is fitted with a common local-call connecting key switch, a common trunk-line holding key switch, and an individual connectin key switch for each trunk line. In Fig. 1, two of the individual trunk-line connecting key switches are shown for each ofstations #20 and #21, which provides sufiicient key switch equipment to illustrate properly the interwiring between the key switches.

Each local station line terminates at the switching equipment in a plunger lineswitch of the well-known lO-trunk self-aligning type such as is disclosed in the patent to Obergfell, No. 1,- 720,342, issued July 9, 1929, wherein the plunger, when released, returns immediately to the control of a master switch. The lineswitch associated with a local station is plunged into a local interconnecting link or a distant-exchange trunk line, as directed by the operation of the related connecting key switch at the local-station telephone, the proper lineswitch bank being selected by the action of the master switch. The master switch is of the well-known solenoid type similar to that disclosed in Patent No. 1,185,510, dated May 30, 1916, in which a U-shaped spring moves the switch wipers step by step in one direction under the control of an escapement and, when the last wiper bank contact has been reached, a solenoid quickly returns the switch wipers back to the starting point.

Each local interconnecting link is permanently wired to two separate trunks of the lineswitch banks, one of these two trunks permitting a calling local station to connect with the link, and the other trunk enabling the calling local station to connect with a desired local station through the link. The distant-exchange trunk lines each have one appearance in the lineswitch banks. The relationship of the links and the distant-exchange trunk lines to the lineswitch bank trunks is shown in simple diagrammatic form in Fig. 8 wherein station A is connected to station B by way of lineswitch Bill, link #1 and lineswitch 8B2: station C to station D by way of lineswitch 803, link #2 and lineswitch 804: station E to trunk line #I by way of lineswitch 805; and station F to trunk line #2 by way of lineswitch 805. It is obvious that other arrangements of links and trunk lines may be employed.

The local-station lines are divided into groups of ten lines each, For example, group #I consists of lines #H) to #19 inclusive, and group #2, of lines #20 to #29 inclusive. Similarly, group #3 consists of lines #30 to #39 inclusive, and so on for other groups. In order to simplify the drawings, this disclosure includes equipment for only stations #20 and #2l of group #2 and for station #30 of group #3. It should be understood, however, that groups #2 and #3 respectively consist of stations #20 to #29 inclusive and stations #30 to #39 inclusive, and that related lineswitches, relays, contacts and wiring, although not shown, are similarly provided. Also, other groups can be included.

It should be further understood that while a plurality of battery connections are shown in the drawings, they are preferably the same battery, Also, in order to simplify the drawings further, details of the ringing current, dial and busy tone generators have been omitted, as well as contacts for closing the starting circuits of the generators.

The relay-type call alotter illustrated in Fig. 2 permits one initiated call from the local stations to be registered at a time for extension to a local interconnecting link or to a distant-exchange trunk line. The three local interconnecting links shown in Fig. 8 are allotted in numerical sequence in the manner well known in conventional allrelay systems. The tens relay 220 is associated with local station group #2, and the tens relay 230 with local-station group #3. Tens relays for other local-station groups would be connected in a similar manner. Ten units relays are provided, but only the first units relay (relay 20l) and the tenth units relay (relay 2l0) are shown in Fig. #2, it being understood that units relays 202 to .209 inclusive would be wired in a manner similar to that shown for relays 20| and 210. The energizing circuits for the tens relays and the units relays are each chained in series circuits through the respective relays for preventing more than one tens relay and one units relay from operating at one time. Hence, a second local station cannot be connected with a local link or a trunk line while another local station is being connected with a local link or a trunk line. The tens relay chain circuit is continued in series through relays 3|0, 320 and 330 of local links #I, #2 and #3 for preventing a local link from connecting a called local station with the link while another station is being connected with a local link or a trunk line, and vice versa.

The six relays designated M0 to 660 inclusive in Fig. 6 register the impulses from a local station making a local call. These relays advance in the well known manner, in accordance with the digit dialed, digit 1 operating relay 610, digit 2 relays 6!!! and 620 in succession, and so on with digit 6 operating relays 6| 0, 620, 630, 640, 050 and 660 in succession. Digit '7 operates relay 6 I0 a second time: digit 8, relays 6l0 and 520 a second time: digit 9, relays 6|0,

-62!) and 630 a second time; and digit 0 relays Bill, 620, 330 and 640 a second time.

Facilities are provided so that certain local stations may be restricted from making outgoing calls over the distant-exchange trunk lines. Provision is also made for conference service on trunk calls.

The invention having been described generally, a detailed operation of the equipment will now be given. For this purpose it will be assumed that the call allotter shown in Fig. 2 has pre-assigned local interconnecting link #I, and that there are no local or trunk calls in progress. With these conditions of operation, the equipment is in the position shown in the drawings.

Local calls Briefly, local calls are completed in the following manner: The person at the calling station lifts the handset piece from the cradle of the telephone, depresses the local-call connecting key into the operated position where it locks and, after receiving dial tone, dials the telephone number of the desired local station. If the called station is not busy, the station will be rung automatically and intermittently. If the called station is in use, the person at the calling station will receive busy tone. The release of the local connection is under the control of the person at the calling station.

In order to describe a local call in detail, it

will now be assumed that station #20 desires to call station #30. Responsive to the lifting of the handset piece and the subsequent depressing of the local-call connecting key at station #20, line relay 20 is operated from ground by way of contact 43 of station #20 lineswitch, conductor 82, contact l3 of local-call connectingv key, direct-current loop through telephone 10, conductor 8|, contact 40 of station #20 lineswitch, winding of relay 20 to negative battery. At armature 24, relay 20 completes the circuit to tens relay 220 from ground by way of contact 35 of station #20 lineswitch, armature 24, conductor 209, winding of relay 220, armatures 225, 24!, conductor 273, armatures 3E5, 325, 335, conductor 214, armatures 235, 221, resistance 2H3 to negative battery. Tens relay 220 operates and locks to ground by way of conductor 209, 'wind-' ing of relay 220, armature 22B, resistance 2E9 to negative battery.

At armature 223, tens relay 220 completes the circuit to units relay 2l0 from ground by way of contact 34 of station #20 lineswitch, armature 23, conductor 268, armature 223, winding of units relay 210, armatures 2E2, 202, 2M, 205, resistance 208 to negative battery. Units relay 2I0 operates and locks to ground by way of conductor 268, armature 223, winding of units relay 2|0, armatures 213, 205, resistance 200 to negative battery. At armature 2H5, units relay 2|0 connects ground to the local start conductor 263 by way of armatures-2H5, 2H, conductor 264, contact I2 of local-call connecting key, conductor 83, armature 2| to local start conductor 263. Ground on the local start conductor 203 completes the circuit to start relay 350 of local interconnecting link by way of armature 246 and working contact, conductor 218, winding of start relay 350 to negative battery, causing start relay 350 to operate. Local interconnecting link #I was pro-assigned for use in this call in the manner described in the following paragraph.

The local interconnecting links are pro-assigned in numerical sequence by means of the call allotter relays 245, 250, 255 and 2:50 operating in a cyclic manner well. known in all-relay systems. Relay 245 is associated with link #l, relay 250 with link #2, relay 255 with link #3, and relay 260 is common to relays 245, 250 and 255. When all four relays are at normal, the circuit to relay 260 is completed from ground, armatures 241, 252, 251, winding of relay 200 to negative battery, causing relay 2% to operate. At armature 2M, relay 250 completes the circuit to relay245 from ground, armature 26L resting contact or armature. 4E, conductor 20:4.

busy switch 355, conductor 345, armature 4I5, conductor 344, conductor 219, upper winding of relay 245 to negative battery Relay 245 operates and locks to ground, lower winding of relay 245, armature 248 and working contact, conductor 284, busy switch 355, conductor 345, armature 4I5, conductor 344, conductor 219, upper winding of relay 245 to negative battery. At armature 246 and working contact relay 245 extends local start conductors 263 and 248 to start relay 350, thereby pre-assigning link #I. In a like manner to that just described for the operation and locking of relay 245, relay 260 also causes relays 2'50 and 25 to operate and lock. At armature 25| and working contact, relay 250 closes a point in the circuit of start relay 355 associated with link #2; and, at armature 255 and working contact, relay 255 similarly closes a point in the circuit of start relay 310 associated with link #3. It is obvious that start relay 360 of link #2 cannot be extended to local start conductors 253 and 249 until relay 245 associated with link #i is restored, and that start relay 318 of link #3 cannot be extended to local start conductors 263 and 249 until both relay 245 associated with link #i and relay 250 associated with link #2 are restored. Relay 245 is restored when link #I is seized by a call origi nated by a, local station, and relay 258 then extends local start conductors 253 and 248 to start relay 360, thereby pre-assigning link #2. In a similar manner, relay 255 extends local start conductors 253 and 249 to start relay 310 when relay 250 restores, thereby pre assigning link #3. When relay 255 restores as link #3 is seized, the circuit to relay 260 is completed from ground, armatures 241, 252 and 251 in series, winding of relay 260 to negative battery, causing relay 250 to operate and again complete the operating circuits to relays 245, 250 and 255. With all three relays 245, 250 and 255 operated and locked, link #I is again pre-assigned to local start conductors 263 and 249. Relay 250 is slow to release, and armatures 248, 253 and 258 are fitted with contacts of the make-before-break type, to insure that relays 245, 253 and 255 will be locked in the operated positions.

Returning now to the description of the call originated at local station #20, start relay 350 is operated in the manner previously described. At armature 353, relay 350 completes the circuit to relay 240 in the call allotter from ground, armature 353, conductor 215, winding of relay 240 to negative battery; and, at armature 35!, connects ground to the contact at the top of master switch bank 428 by way of conductor 342 to mark the answering end of link #I in master switch bank 428. At armature 352, relay 350 completes the circuit to lock magnet 490 of the master switch from ground, armature 352, conductor I66, armature 486, winding of lock magnet 490 to negative battery; and, at armature 354, completes a multiple holding circuit to relay 245 to insure that relay 245 will remain locked until start relay 350 is restored. The ground on the top contact of master switch bank 428 completes the circuit to stop magnet 485 by way of contact 483 of trip magnet 485, causing stop magnet 485 to operate and open the circuit to lock magnet 490 at armature 485 beforelock magnet 490 has had sufiicient time to operate. The master switch, therefore, does not move from the bank position shown in Fig. 4, and the plungers of all lineswitches are aligned with the correspondin trunk to the answering end of link #I.

The operation of stop magnet 485 also completes the circuit to pull-down magnet 40 of station #20 lineswitch from ground by way of armature 488, conductor 212, armatures 2| I, 22 I, conductor 210, conductor 254, winding of pull-down magnet 40 to negative battery, the operation of pull-down magnet 40 causing the plunger of station #20 lineswitch to plunge into the bank trunk connected to the answering end of link #I. The direct-current loop of station #20 telephone is thus extended to link #I by way of conductor 8|, bank contact 50', conductor I1I, upper winding of line relay 405, negative battery, ground, lower winding of line relay 405, conductor I12, bank contact 52', conductor 82, and contact I3 of localcall connecting key, causing line relay 405 in link #I to operate.

The operation of pull-down magnet 40 also operates contacts 32, 33, 34, and 35 through the medium of armature 3|, and contacts 42, 43 and 44 through the medium of armature 4 I. Contact 43 completes a holding circuit for pull-down magnet 40 from ground, contact 43 and working spring, contact I2 of local-call connecting key, conductor 83, bank contact 5|, conductor 254, winding of pull-down magnet 40 to negative battery, thus retaining station telephone #20 connected to link #I as long as the calling person keeps the handset piece from the telephone cradle. At the resting spring of contact 43, ground is removed from line conductor 82; and, at contact 44, line relay 20 is disconnected from line conductor 8|, causing line relay 20 to restore. The line circuit of station #20 is now clear of attachments. At contact 34, the circuit to units relay 2|0 is opened, causing units relay 2|0 to restore; and, at contact 35, the circuit to tens relay 220 is opened, causing tens relay 220 to restore. Contacts 42, 32 and 33 perform no functions at this time. Line relay 20 restoring opens additional points in the circuits to tens relay 220 and units relay 2|0 at armatures 24 and 23 respectively, and, at armature 2|, removes ground from local start conductor 283, causing start relay 350 to restore.

The operation of line relay 405 in link #I completes the circuit to relay 4 I 0 from ground by way of bank contact 53', conductor I13, armature 406, winding of relay M0 to negative battery, causing relay M0 to operate and lock to ground on conductor I13 by way of armature 4I2. At armature 4|4, relay 4I0 completes the circuit to relay 435 from ground, armatures 4 I4, 423, winding of relay 435 to negative battery, causing relay 435 to operate; and, at armature 4I5, opens the circuit of relay 245 in the call allotter, causing relay 245 to restore. At armature 246 and resting contact, relay 245 transfers local start conductors 263 and 249 to start relay 350 of link #2. The restoration of relay 245 makes link #I busy to other calls because the circuit to start relay 350 is open at the working contact of armature 246.

At armature 35I, start relay 350 of link #I upon restoring removes ground from the top contact of master switch bank 428, causing stop magnet 485 to restore: at armature 352, opens the circuit to lock magnet 490 (now closed at armature 486) before lock magnet 490 has had sufficient time to operate; and, at armature 353, opens the circuit to relay 240 of the call allotter. The call allotter is now in a position to accept another call, with link #2 pre-assigned to local start conductors 263 and 249. The restoration of tens relay 220 and units relay 2 I open additional points in the circuits previously opened by the restoration of line relay 20.

Dial tone is returned from link #I to the calling person at station #20 by way of armatures 583, 563, conductor 414, armature 436, and condenser 408 as a signal to dial the number of sta: tion #30. When the calling person at station #20 dials the digit 3, line relay 405 in link l correspondingly de-energizes and re-energizes three times. With the first de-energization of line relay, 405, the circuit to relay 425 is completed from ground, armatures 401, 413, 42-2, winding of relay 425 to negative battery, causing relay 425 to operate. A multiple circuit is also completed from armature 401 by way of arma tures M3, 422, conductor 341, armatures 69l, 586 GM and associated resting contacts, winding of register relay 6I0 to negative battery, causing relay 640 to operate and lock to ground by way of armatures 4M, 44!, conductor 442, armature 681, winding of relay 680 and armature 613, relay- 680 operating on this locking circuit. The second re-energization of line relay 405- completes the circuit to register relay 620 from ground, armatures 401, 4&3, 4-22, conductor 341, armatures 69!, 686 and associated resting contacts, armature 68! and working contact, armature 6I4, winding of register relay 620 to negative battery, causing register relay 620 to operate and look from ground, armatures 414', 44l,' conductor 442, armature 6'92, winding of relay 685 and armature 624, relay 685 operating on this locking circuit. At armature 681, relay 685' opens the locking circuit to relays 680 and 6l0', causing these two relays to restore. The third de-energization of line relay 405' completes the circuit to register relay 630 from ground, armatures 401, M3, 422, conductor 341, armature 69l and resting contact, armature 686 and working contact, armature 625, winding of register relay 630 to' negative battery, causing register relay 630 to operate and look from ground, armatures 4M, 44!, conductor 442, armature 682, winding of relay 690 and armature 634', relay 690' operating on this locking cir-' cuit. At armature 692, relay 690 opens the locking circuit to relays 685 and 620', causing these two relays to restore. Shortly after'th'e third reenergization of line relay 405, relay 425 rest'o'res, its slow-to-release action preventing its release during the dialling of the digit 3.

At armature 421, relay 42'5 completesthe circuit to relay 560 from ground, armature 59'3", conductor 348, armatures 421, 451 and resting. contact, conductor 444, armature 633, conductor 616, windin of relay 560 to negative battery, causing relay 560 to operate. At armature 553, relay 560 opens the dial tone circuit to station #20. At armature 56!, relay 560 completes the circuit to relay 440 from ground, armature 414, conductor 4S3, armature 56L conductor 434, armature 455', winding of relay 440' to negative battery, causing relay 449 to operate. At armature 4'4l, relay 4 40 opens the locking circuit to relays 690 and tan, causing these two relays to restore. As a result of relay 630 restoring and; at armature 633; re"-' moving ground from the'winding of relay '60, rel'ay'45-5 operates in series with relay 560' over the circuit from ground; armature 414', winding of re1ay'455; conductor 439; armature 562, winding of relay 550 to'negativebattery, this" circuit'al'slo retaining relay 560'in' the operated position. At armature 456-, relay 4'55 opens-the'circuitto relay 4'40; causing relay 440 to restore The register" 10 relays are now iii position to receive the second digit from the calling station.

Wheri the calling person at stat on #20 dials the second digit '0, line relay 405 in link #1 correspondingly file-energizes and re-energizes ten times. With the first de-energization of line relay 405, the circuit is completed to relay 425 from' ground, rma ures 401, 413, 422, winding of relay 425 to negative Battery, causing relay 425 to operate. A. multiple circuit is also completed from arrnature 4G! to register relay 6H1, causing register relay tlt to' operate and lock in series with relay 6'80 in the manner previously described. The second de-e'nergizatiori of line relay 405 causes registerr'elaytn' to operate and lock in seriesl with in the manner previously described. At rmature 6'31, relay 685 opens the locking circuit to re'la'yst afl and 610, causing these two reiays to restore. The third de-energization of line relay 4'05 causes reg istr relay 630 to operate and lock in se ies with relay can in the manner previously described. At armat ure 6912, relay 500 opens the locking circuit to relays cat and 620, causing these tworelay's' to restore. The fourth de energiz'ation of line relay 405 completes the circuit to tegistetreiay 64 from ground, arma tures 4il1, 4l3, 422, onductbr 341, armature 94 and working contact, armature fi35, Winding of register relay 649 to negatiye battery, causing relay 64K? to operate and lo'ckj t'o ground by wayoi conductor 442, armature 6'81, winding of relay E80, and armature B43, relay 600" operating on this locking circuit. At armature 6'82, relay 680 opens the locking circuit torelays' can and 630'. The fifth de eriergization of line relay 405 completes the circuit t g register relay 650 from ground, armatures 401, 41 3', 4'22, conductor 3 41', armatures 691, fifiliand ass'obiatd resting contacts, armature set and working contact, armature 6'44, winding of relay 650 to negativebattry, causing relay 6'50 to operate and lock to ground lay way or conductor 442, armature 602i, winding of relay $05, and armature 6'52, relay 585 operating on this l'ocking circuit. At armature 081, relay E8 5 opens the lockingcircuit tore'lay treat-t1 640.

The sixth de-ene'rgization of line relay 405" completes' the circuit to register relay 6'60 from ground", armatures 401, 413,: 422', conductor 34?, armature 6'91 and resting contact, armature 086 and working contact; armature 6'53, winding of relay 600 to negative battery, causing relay est tooperateand lock to ground by way of conductor 4'42, armature 6'82, winding of relay 690' and armature 06$, relay' can operating on this locking Gilcuit. At armature 59'2, relay 090 opens" the looking ci rcuit'torel'ay's sits and 650. At armature 662-, relay 65'0" completes circuit to relay 6'10 from roundyarmatur s 414, 45a, conductor 4:43; armature tz, winding of relay 610 to negative battery, causing that tiu tttetate' and lock to round on conductor 443 16y way of armature 615. The seventh de energization of line relay 40s" completes the circilit to register rela'y sin from round; a matures" 401.; m, 422, conductor 341, armature 09! and'vvorking contact, armature 664, winding." of relay am o negative battery, u in relays m to operate and lock to ground by way ofc'onductor 442, armatureifitll, winding y of relay eat; and armature tas, relay tat oper ating on this locking circuit. At armature 6232, relay 65o ope-nth the lh'cking circuits" to relays B and 660, The eighth teeter-a tach of line relay" 405 causes register relay 020 to" operate and loc'l' in serieswith" relay to 5 at th manner previously described? At armature 6'81, relaytilfi opens the locking circuits to relays 680 and 610. The ninth de-energization of line relay 405 causes register relay 630 to operate and lock in series with relay 690 in the manner previously described. At armature 692, relay 690 opens the locking circuit to relays 685 and 620. The tenth de-energization of line relay 405 causes register relay 640 to operate and lock in series with relay 680. At armature 682, relay 680 opens the locking circuits to relays 690 and 630.

Shortly after the tenth re-energization of line relay 405, relay 425 restores, its slow-to-release action preventing its release during the dialling of the digit 0. At armature 421, relay 425 completes the circuit to relay 420 from ground, armature 683, conductor 348, armatures 421, 451 and working contact, winding of relay 420 to negative battery, causing relay 420 to operate. At armature 424, relay 420 connects the winding of busy relay 445 to the winding of pull-down magnet 540 of the dialled station #30 by way of armature 438 and working contact, armatures 426, 424, conductor 346, armature 611 and working contact, armature 642, conductor 643, and armature 510, but neither busy relay 445 or pull-down magnet 540 can operate under this condition as both are connected to negative battery.

Should station #30 be in use at this moment, pull-down magnet 540 would have been operated by ground On conductor 554, and this ground multipled to armature 510 will now operate busy relay 445 by way of conductor 648, armatures 642, 611 and working contact, conductor 346, armatures 424, 426, 438 and working contact (before relay 435 has time to restore due to its circuit being opened at armature 423), winding of busy relay 445 to negative battery, causing busy relay 445 to lock to ground by way of armatures 414,-

and 441 and working contact. At armature 446, busy relay 445 extends busy tone to the station telephone to inform the calling person that station is in use.

Should station #30, however, not be in use at the moment, busy relay 445 in line #1 will not operate because the negative battery through the winding of busy relay 445 meets the negative battery through pull-down magnet 540 of the dialled station #30. Under this condition, relay 435 upon restoring shortly afterward because its circuit was opened at armature 423, completes the circuit to relay 310 from ground, armatures 414, 441 and resting'contact, 451, 431, 421, conductor 343, winding of relay 310, armatures 313, 315, 325, 335, conductor 214, armatures 235, 221, resistance 219 to negative battery. Relay 310 operates and locks to ground on conductor 343 by way of winding of relay 310, armatures 314, 325, 335, conductor 214, armatures 235, 221, resistance 219 to negative battery. Relay 310 is wired in the chain circuit of the tens relays 220 and 230 (Fig. 2) in the call allotter in order that the master switch will be operative by one call at a time. At armature 311, relay 310 grounds the fourth contact from the top of master switch bank 428 by way of conductor 339; and, at armature 312, completes the circuit to lock magnet 490 of the master switch from ground, armature 312, conductor 166, armature 486, Winding of lock magnet 490 to negative battery, causing lock magnet 490 to operate.

The operation of lock magnet 490 causes armature 491 to disengage lock lever 492 from the tenth notch in sector 416, and U-spring 489 drives sector 416 counter-clockwise, sector 416 being pivoted at 411. As Wiper 428 of the master switch makes contact with the fourth contact from the top of bank 428, the circuit to stop magnet 485 is completed from ground, armature 3| 1, conductor 339, wiper 428 in engagement with the fourth contact from the top of bank 428, contact 483 of trip magnet 480, winding of stop magnet 485 to negative battery. The operation of stop magnet 485 opens the circuit to lock magnet 490 at contact 486, causing armature 491 to restore and permit lock lever 492 to engage the fourth notch from the right in sector 416, thereby arresting the motion of sector 416. The plungers of all idle lineswitches (in this disclosure the plungers of lineswitches #21 and #30) are correspondingly aligned by the master switch shaft in the well-known manner opposite the bank trunk connected to the calling end of link #1. As wiper 429 of the master switch makes contact with the fourth contact from the top of bank 429, the circuit to the pull-down magnet 540 of the dialled station #30 is completed from ground, armature 481, wiper 429 in engagement with the fourth contact from the top of bank 429, resting contact of armature 452, armatures 448, 438, 426, 424, conductor 346, armature 611 and working contact, armature 642, conductor 648, armature 5'10, winding of pull-down magnet 540 to negative battery, the operation of pull-down magnet 540 causing the plunger of station #30 lineswitch to plunge into the bank trunk connected to the calling end of link #1. Conductors 411 and 412 of link #1 are thus extended to station #30 line circuit by way of bank contact 550 and 552 respectively, and the circuit to relay 450 is completed from ground, bank contact 553, conductor 413, winding of relay 450 to negative battery, causing relay 450 to operate. At armature 451, relay 450 opens the circuit to relay 310, causing relay 310 to restore. The restoration of relay 310 frees the call allotter and the master switch for use in another call. At armature 452 and working contact, relay 450 shifts the holding circuit of pull-down magnet 540 to ground by way of armature 414.

The operation of pull-down magnet 540 also operates contacts 532, 533, 534 and 535 through the medium of armature 531, and contacts 542, 543 and 544 through the medium of armature 541. At the resting spring of contact 543, ground is removed from line conductor 582; and, at contact 544, line relay 520 is disconnected from line conductor 581. The line circuit of station #30 is thus cleared of attachments in preparation of the ringing circuit to station #30 telephone 510. Contacts 532, 533, 534, 535 and 542 perform no functions at this time. The ringing loop to station #30 telephone 510 is completed from ground in link #1 by way of armature 431 and resting contact, conductor 411, bank contact 550, conductor 581, ringer loop in telephone 5111, conductor 582, bank contact 552, conductor 412, armature 433 and resting contact, upper winding of ringing cut-off relay 430 to interrupted generator. The ringer at station #30 telephone 510 is operated automatically and intermittently until the called station answers or the calling person at station #20 abandons the call.

Responsive to the closing of the direct-current line loop when the handset piece at telephone 510 is lifted from the cradle and the related localcall connecting key is depressed, ringing cut-01f relay 430 operates and locks to ground by way of armatures 411 and 432. At the resting contacts of armatures 431 and 433, relay 430 disconnects the ringing current from station #30 line circuit;

for pull-down magnet 540 to be completed from ground, working spring of contact 543, contact 5I2 of local-call connecting key, conductor 583, bank contact 55!, conductor 554, winding of pull-down magnet 540 to negative battery.

After the conversation between the persons at stations #20 and #30 has been completed, and responsive to the calling person at station #20 returning his handset piece to the telephone cradle, the local-call connecting key at telephone I is automatically released and returns to the normal position. The holding circuit of pulldown magnet 40 is, consequently, opened at contact l2 of the local-call connecting key, and the plunger of station #20 lineswitch is withdrawn from the bank trunk leading to the answering end of link #I. The bank contacts 50', 5|, 52' and 53' are opened by the withdrawal of station lineswitch plunger, and the plunger is automatically aligned with the shaft of the master switch in the well-known manner. Responsive to the called person at station returning his handset to the cradle, the local-call connecting key at telephone 510 is automatically released and returns to the normal position, opening the multiple holding circuit to pull-down magnet 540 at contact 5l2. Pull-down magnet 540, however, is held in the operated position over the circuit through armature 510 of relay 560.

The restoration of armature 4| by the release of pull-down magnet opens an additional point in the circuit of pull-down magnet 40 at the working spring of contact 43: at contact 43 and resting spring, connects ground to line conductor 82 of station #20; and, at contact 44,

connects line relay 20 of station #20 lineswitch to line conductor 81. Theline circuit of station #20 is now at normal.

Line relay 405 of link #I is restored when its loop circuit is opened by the replacement of the handset piece on the cradle at station #20. The locking circuit to relay 410 of link #I is opened at bank contact 53', and relay 4I0 restores. At armature 4| I, relay 410 opens the locking circuit to ringing cut-01f relay 430, causing relay 430 to restore. At armature 414, relay 410 opens the holding circuits to relays 455 and 560 in series, the holding circuit to relays 680 and 640 in series, the holding circuit to relay 610, and the holding circuit to pull-down magnet 540 of station #30 lineswitch, causing these five relays and pulldown magnet 540 to restore. At armature 451, relay 455 opens the circuit to relay 420, relay 420 restoring.

The restoration of pull-down magnet 540 of station #30 lineswitch causes the withdrawal of p the associated plunger from the bank trunk leading to the calling end of line #I. The bank contacts 550', 55l, 552' and 553' are opened by the withdrawal of station #30 lineswitch plunger, and the plunger is automatically aligned with the shaft of the master switch. The circuit to relay 450 is opened at bank contact 553', and relay 450 restores. Link #I is now in the normal position, available for re-assignment to 14 other calls in numerical sequence with links #2 and #3.

The restoration of armature 541 by the release of pull-down magnet 540 opens an additional point in the circuit of pull-down magnet 540 at the working spring of contact 543: at contact 543 and resting spring, connects ground to line conductor 582 of station #30; and, at contact 544, connects line relay 520 of station #30 lineswitch to line conductor 58!. The line circuit of station #30 is now at normal.

Local interconnecting links #2 and #3 are also used to complete local connections in a manner similar to that just described for link #1 with the minor exceptions that start relays 360 and 310 respectively are employed instead of start relay 350, and correspondingly related bank contacts are utilized instead of the bank contacts mentioned in the foregoing description.

Outgoing trunk: calls Any non-restricted local station may originate an outgoing trunk call to the distant exchange by lifting the handset piece from the telephone cradle and depressing one of the trunk-line connecting keys into the operated position where it looks. If the trunk line thus selected is in use, busy tone will be returned to the telephone at the calling local station, and the calling person thereupon depresses another trunk-line connecting key, the operation of the latter key automatically releasing the first mentioned connecting key. Assuming now that the second selected trunk line is free, then the calling person is connected through to the distant exchange over that trunk line, and dial tone is returned to the calling person if the distant exchange is of the automatic type, or an operator responds to the call if the distant exchange is of the manual type.

Assuming further that the selected free trunk line is trunk line #I, that the call is originated at station #30, (Fig. 5) and that no other calls are in progress, then line relay 520 is operated from ground by way of contact 543 of station #30 lineswitch, conductor 582, contact 515 of trunk-line #1 connecting key, direct-current loop through telephone 5l0, conductor 58L contact 544 of station #30 lineswitch, winding of from ground by Way of contact 535 of station #30 lineswitch, armature 524, conductor 209 in cable 285 through Figs. 6 and 3 to Fig. 2, conductor 209 in Fig. 2, winding of relay 230, armatures 233, Ml, conductor 213, armatures 3l5, 325, 335, conductor 214, armatures 235, 221, resistance 219 to negative battery. Tens relay 230 operates and locks to ground by way of conductor 209, winding of relay 230, armatures 234, 221, resistance 2l9 to negative battery.

At armature 23Z, tens relay 230 completes the circuit to units relay 2 I0 from ground by way of contact 534 of station #30 lineswitch, armature 523, conductor 219 in cable 235 through Figs. 6 and 3 to Fig. 2, conductor M9 in Fig. 2, armature .232, winding of units relay 210, armatures 2l2, 242, 2l4, 205, resistance 200 to negative battery. Units relay 210 operates and locks to ground by way of conductor 219, armature 232, winding of units relay 210, armatures 2I3, 205, resistance 208 to negative battery. At armature 216, units relay 2l0 connects ground to trunk start relay of trunk line #I by way of armatures 21B,

tact I4 of trunk-line #1 connecting key, armature 525, conductor 183, armature 114 and resting contact, winding of relay 188 to negative battery, causing relay 188 to operate. At armature 182, relay 188 connects ground to the fourth contact from the leftof masterswitch bank 428 by way of conductor I65 to mark trunk line #I in master switch bank 428. At armature 18I, relay 188 completes the circuit to lock magnet 498 of the master switch from ground, armature 18I, conductor I66, armature 486, winding of lock magnet 498 to negative battery. The operation of lock magnet 488 causes armature 49I to disengage lock lever 492 from sector 41-6, and U-spring 488 drives sector 416 counter-clockwise.

Assuming now that wiper 428 of the master switch is in engagement with the third contact from the left of bank 428 (this bank contact representing trunk line #2) when lock lever 492 is withdrawn from sector 416, then the counterclockwise motion of sector 416 causes wiper 428 to successively engage the second bank contact from the left and then the first contact. At this point, finger 418 of sector 416 is almost in mechanical contact with finger springs 484 associated with trip magnet 488. Further counterclockwise movement of sector 416 causes sector finger 418 to close the contacts of finger springs 484, and the circuit to trip magnet 488 is thereby completed from ground, contact 494' of lock magnet 498, finger springs 484, winding of trip magnet 488 to negative battery, causing trip magnet 488 to operate. At contact 482, trip magnet 488 completes the circuit to solenoid 415, and solenoid 415 overcomes the power in U-spring 488, driving ector 416 clockwise. Just after this reverse movement of sector 416 is started, sector finger 418 moves from engagement with finger springs 484, but latch M8 is in mechanical engagement with the tip of the operating spring of contact 482, thus retaining armature 48I and contact 482 operated in the manner well known in this type of master switch. Hence, the circuit to solenoid 425 remains complete at contact 482.

As sector 416 reaches its extreme clockwise position, sector finger 418 lifts the spring attached to latch 4l8 sufficiently to release latch 4I8 from engagement with the operating spring of contact 482. Armature 48I is thus restored and the circuit to solenoid 415 is opened at contact 482. At this point, U-spring 488 starts driving sector 416 counter-clockwise because lock magnet 498 is still in the operated position and sector 416 is free from lock lever 492. As wiper 428 makes contact with the fourth contact from the left of bank 428, the circuit to stop magnet 485 is completed from ground, armature 182, conductor I65, fourth contact from the left of bank 428, wiper 428, contact 483, winding of stop magnet 485 to negative battery, causing stop magnet 485 to operate. The operation of stop magnet 485 opens the circuit to lock magnet 498 at contact 486, causing armature 49I to restore and permit lock lever 492 to engage the fourth notch from the left in sector 41-6, thereby arresting the motion of sector 416. The plungers of all idle lineswitches are now aligned opposite the bank trunk connected to trunk line #I.

The operation of stop magnet 485 also completes the circuit to pull-down magnet 548 of station #38 lineswitch from ground by way of armature 488, conductor 212, armatures 2I I, 23I, conductor 288 in cable 285 through Figs. 3 and 6 to Fig. 5, conductor 288 in Fig. 5, winding of pull-down magnet 548 to negative battery, the operation of pull-down magnet 548 causing the plunger of station #38 lineswitch to plunge into the bank trunk connected to trunk line #I. The direct-current loop of station #38 telephone is thus extended to trunk line #I by way of conductor 58I, bank contact 558 conductor I6I, upper winding of relay 188, armature 132 and resting contact, conductor 181, trunk line #I line relay loop at the distant exchange, conductor 182, armature 134 and resting contact, lower winding of relay 168, conductor I62, bank contact 552 conductor 582, and contact 5I5 of trunk-line #I connecting key, causing the line relay at the distant exchange to operate in a conventional manner. Relay 168 does not operate over the circuit just traced because its windings are differentially connected and now oppose each other. The closing of bank contact 553 completes the circuit to relay 118 from ground, bank contact 553 conductor I83, winding of relay 118 to negative battery, causing relay 118 to operate. At the resting contact of armature 1114, relay 118 opens the circuit to trunk start relay 188, causing relay 188 to restore: at armature 114 and working contact, switches trunk start conductor 183 to conductor I64, thereby making trunk line #I busy to other calls; and, at armature 112, disconnects ringing relay 128 from across the trunk line, thus clearing the trunk line of attachments.

The operation of pull-down magnet 548 also operates contacts 532, 533, 534 and 535 through the medium of armature 53I, and contacts 542, 543 and 544 through the medium of armature 54I. Contact 543 completes a holding circuit for pull-down magnet 548 from ground, contact 543 and working spring, contact 5I4 of trunkline #I connecting key, conductor 584, bank contact 55I conductor 554, winding of pulldown magnet 548 to negative battery, thus retaining station #38 telephone connected to trunk line #I as long as the calling person keeps the handset piece from the telephone cradle. At the resting spring of contact 543, ground is removed from line conductor 582; and, at contact 544, line relay 528 is disconnected from line conductor 58I, causing line relay 528 to restore. The line circuit of station #38 is now clear of attachments. At contact 534, the circuit to units relay 2I8 is opened, causing units relay 2!!! to restore; and, at contact 535, the circuit to tens relay 238 is opened, causing tens relay 238 to restore. Contacts 542, 532 and 533 perform no functions at this time. Line relay 528 restoring opens additional points in the circuits to tens relay 238 and units relay 2) at armatures 524 and 523 respectively; and, at armature 525, removes ground from trunk start conductor 183.

At armature 182, relay 188 of trunk line #I upon restoring removes ground from the fourth contact from the left of master switch bank 428, causing stop magnet 485 to restore; and, at armature 18I, opens a point in the circuit to lock magnet 498. The call allotter is now in a position to accept another call. The restoration of tens relay 238 and units relay 2I8 opens additional points in the circuits previously opened by the restoration of line relay 52 8.

Should the distant exchange be of the automatic type, dial tone is returned to the calling person at station #38 as a signal to proceed with the dialling. In response to the dialling at station #38, the switches in the distant exchange 1 7" are; operated in the well-known manner to compl'e'tethe connection desired. Transmission battery'isfsuppliedto'station #30 telephone from the distant exchange.

Should the distant exchange be of the manual type, the operation of the line relay at the distant exchange causes the related line signal on the manual switchboard to indicate that a call is awaiting: attention on trunk line #4. In response to the operator at the distant exchange answering the call, the calling person at station #30' advises the operator of the connection desired, and thereupon" the operator proceeds with the completing of the desired connection in the well-known manner. In this instance also, transmission battery issupplied to station #30teleph'one from the distant exchange.

After the conversation between station 30 an'dthe distant exchange has been completed, and responsive to the callingv person at station #30 shaft of the master switch in the well-knownmanner; The opening of the direct-currentloop to the di's'tant'exch'ange by the replacement of the handset piece on the cradle at station #30 causes the equipment at the distant exchange to be restored". If the distant exchange is of the automatic type, the switchesare released in the wellknown' manner and trunk line #'I is made available. for other calls.- In the case where the distant exchange is manual,.the operator receives disconnectsupervision when the calling person at. stat'i'on. #BB replaces the handset piece on the cradle.

At bank contact 553 the circuit to relay Iiis opened; causing relay. III to restore. At armature TM and resting contact, relay I'Ifi switches trunk start relay I88 to truck start conductor I83,

thus making trunk line #I' available to calls-from local'stations. At armature I12 and resting contact, relay 7-10 bridges ringing. relay I29 across trunk line #I', making trunk line #I available to calls from the distant exchange.

The restoration of armature 54 t by the release of pull down magnet opens anadditional point in the. circuit of pull-down magnet M0 at the working spring. cf contact 3: at contact 543 and resting spring, connects ground to line conductor 532 of station #39 and, at contact 5%,

connects line relay 520. of station #30 lineswitchto line conductor 581'. #60 is now at normal.

The line circuit of station Considering now the case where trunkline #I is in useat the time the trunk-line #1 connecting key atst'ation #tii is depressed for the origination of outgoing callto the distant exchange, then the operation of line relay 52-8 ofstation #30 lineswitch does not complete the circuit to trunk start relay I85 of trunk line #I through contact 51'4' of trunk-line #1. connecting'key, contact 525- of line relay 521'! and trunk start conductor I83 as was previously described for the case where trunk line #i'I was not in use. Instead, ground on trunk start conductor I83 by way of contacts 5M and 525 is extended through armature I'M and working contact, conductor I5 3, armatures H5,

- other relay in the trunk-line circuit.

236', conductor 238 in cable 285 through Figs. 3 an'd'6 to. Fig. 5, conductor- 233' in Fig. 5 to winding of cut-ofi magnet 530" of station #30 lineswitch and negative battermthuscausing cut-off magnet 530 to operate. In this instance, the plunger of. lineswitch #tt: does not plunge into the bank trunk connected to. trunk line #I because cut-off magnet 530' operates armature 53 I only. Cut-01f magnet 53%.? locks to ground by way of contacts 533 and 522,.andf connects busy tone to line conductor 581 by way of contacts 5 32 and 532 to inform the calling. person that trunk line #I is in use. The handset piece is then replaced on the cradle to' open the circuit of line relay 520 which in turn opens the locking circuit of cut-oii magnet. 530 at armature 522, and cut-off magnet 530 restores and disconnects busy tone from line conductor 58.! at contact 532*. The calling person at station #30" may then originate a trunk call' over another trunk line by lifting'the handset piece and depressing a trunk-line connecting key other than trunk-line #I' connecting key.

Considering now the case where a local station is restricted from making outgoing calls to the distant exchange, the trunk start conductors from the lineswitch of. such a restricted station are not connected to the respective trunk start relays (such as relay I00 through armature I14 and resting contact for trunk line #I). Instead, each trunk start conductor from the respective contact of the restricted stations lineswitch is connected to an armature of am For example, station #2! is indicated as being restricted from making outgoing calls to the distant exchange; and trunk start conductor I51 from contact I25 of line relay I20 is shown connectedto armature H3 of trunk line #I instead of to armature II i as is the case of start conductor I83 from contact 525 of line relay 520.. Now, when the calling person at station #ZI liftsthe handset piece from the cradle and depresses trunk-line #I connecting key, the circuit to cutoff magnet. I30 of station #ZI lineswitch is completed from ground by way of armatures 20.1, 2I8, conductor 252,.contact IIII of trunk-line #1 connecting key, armature I25, conductor "51, armature II3 and resting. contact, armature I35 and resting contact, conductor I64, armatures 206, 229, conductor 265', winding of cut-ofi magnet I=30to negative battery, causing cut-off magnet I30 to' operate. In this instance, the plunger of lineswitch #ZI does not plunge into the bank trunk connected to trunk line #I because cutofi magnet I30 operates armature I3I only. Cutoii magnet I30 locks to ground by way of contacts I33 and I 22', and connects busy tone toline conductor I 8I' by way of contacts M2 and I32 to inform the calling person that he cannot connect with trunk line #I. Should the calling person then attempt to connect with the other trunk lines, busy tone will be returned in each instance. 7

Incoming trunk calls It will-now be assumed that an incoming trunk call is received over conductors 'I0l and I02 of trunk line #I from the distant exchange. Ringing. current by way of conductor IOI, condenser 'II I', winding of ringing relay I20, armature I12 and conductor I02 causesringing relay I20- to operate. At armature I2I, relay I20 completes the circuit to relay 'IIII', causing relay H0 to operate and lock to ground by way of armatures 11 3 and H2. At armature III, relay H0 complete's'the circuit to trunk line #I incoming call signal, or signals, to advise the local stations that an incoming call on trunk line #I is awaiting attention. At the resting contact of armature II3, relay H disconnects trunk start conductor I6I from armature I35; and, at armature H3 and working contact, extends trunk start conductor IEI to the winding of trunk start relay I80 to make it possible for station #2! to answer this trunk call. Stations #20 and #30 are already in a position to answer this trunk call, as trunk start conductor I06 is connected directly to the winding of trunk start rela'y I80, and trunk start conductor I83 is connected to the winding of trunk start relay I80 through arma-- ture I14 and resting contact.

Assuming further that a person at station #2! decides to answer this trunk call, then the lifting of the handset piece at telephone II 0 and the depressing of the related trunk-line #I connecting key completes the circuit to line relay I20, and the operation of line relay I20 causes the subsequent operation of tens relay 220 and units relay 20I in a manner similar to that described in the preceding section titled Outgoing trunks calls for the operation of tens relay 220 and units relay 250. The operation of tens relay 220 and units relay 20I completes the circuit to trunk start relay I80 from ground, armatures 201, 2H3, conductor 262, contact II of trunk-line #I connecting key, armature I25, trunk start conductor I61, armature H3 and working contact, winding of relay 700 to negative battery, causing relay I80 to operate. At armature I82, relay I80 connects ground to the fourth contact from the left of master switch bank 428 by way of conductor I65 to mark trunk line #I in master switch bank 428. At armature I8I, relay I80 completes the circuit to lock magnet 490 of the master switch from ground, armature I8 I, conductor I66, armature 486, winding of lock magnet 400 to negative battery. The master switch accordingly moves the plungers of all idle lineswitches into alignment with the bank trunk connected to trunk line #I in the manner described in the preceding section titled Outgoing trunk calls.

The operation of stop magnet 085 when wiper 428 of the master switch engages the fourth contact from the left of bank 420 completes the circuit to pull-down magnet I40 of station #3I lineswitch from ground, armature 588, conductor 212, armatures 202, 222, conductor 2? I, conductor 259, winding of pull-down magnet I40 to negative battery, the operation of pull-down magnet I40 causing the plunger of station #2 I lineswitch to plunge into the bank trunk connected to trunk line #I. The direct-current loop of station #2! telephone is thus extended to trunk line #i by way of relay conductor I8I, bank contact I50 conductor IIiI, upper winding of relay I60, armature I32 and resting contact, conductor 10!, supervisory and transmission battery loop at the distant exchange, conductor I02, armature 734 and resting contact, lower winding of relay I60, conductor I62, bank contact I52 conductor I82 and contact H of trunk-line #I connecting key. Relay I60 does not operate over the circuit just traced because its windings are differentially connected and now oppose each other. The closing of bank contact I53 completes the circuit to relay II0 from ground, bank contact I'53 conductor I63, winding of relay I70 to negative battery causing relay 'II0 to operate. At the resting contact of armature I'I l, relay II0 opens one circuit path to trunk start relay I80: at armature I'M and working contact, switches trunk start conductor I83 to conductor I64, thereby making trunk line #I busy to calls from other local stations associated with start conductor I83: at armature I13, disconnects ground from the locking circuit to relay IIO, causing relay H0 to restore; and, at armature II2, disconnects ringing relay I20 from across the trunk line. At armature II I, relay I10 opens the circuit to the incoming call signal, or signals: at the working contact of armature II3, opens the circuit to trunk start relay I80, causing relay I80 to restore; and, at armature H3 and resting contact, switches trunk start conductor I61 to conductor I64 by way of armature I35 and resting contact, thereby making trunk line #I busy to other calls over conductor ISI.

The operation of pull-down magnet I40 also operates contacts I32, I33, I34 and I35 through the medium of armature I3I, and contacts I42, I43 and I44 through the medium of armature I4I. Contact I43 completes a holding circuit for pull-down magnet I40 from ground, contact I43 and working spring, contact H4 of trunk-line #I connecting key, conductor I84, bank contact I5I conductor 259, winding of pull-down magnet I40 to negative battery, thus retaining station #ZI telephone connected to trunk line #I as long as the person at station #2I keeps the handset piece from the telephone cradle. At the resting spring of contact I43, ground is removed from line conductor I82; and, at contact I44, line relay I20 is disconnected from line conductor I8I, causing line relay I20 to restore. At contact I34,

the circuit to units relay 20I is opened, causing" units relay 20I to restore; and, at contact I35, the circuit to tens relay 220 is opened, causing tens relay 220 to restore. Contacts I42, I32 and I33 perform no functions at this time. At armature I82, relay I80 upon restoring removes ground from the fourth contact from the left of masterswitch bank 428, causing stop magnet 485 to restore; and, at armature I8I, opens a point in the circuit to lock magnet 490. The call allot- Transmission battery is supplied to station #2I telephone from the distant exchange.

After the conversation between station #ZI and the distant exchange has been completed,

I and responsive to the person at station #ZI returning his handset piece to the telephone cradle, the trunk-line #I connecting key at telephone I I0 is automatically released and returns to the normal position. The holding circuit of pull-down magnet I40 is opened at contacts I I4 of trunk-line #I connecting key, and the plunger of station #21 lineswitch is withdrawn from the bank trunk connected to trunk line #I. The bank contacts I50 I5I I52 and I53 are opened by the withdrawal of station #ZI lineswitch plunger, and the plunger is automatically aligned with the shaft of the master switch. At bank contact I53 the circuit to relay I10 is opened, and relay IIIJ restores. At armature H4 and resting contact, re-

,\ lay I10 switches trunk start relay I to trunk In order to describe how persons at local stations can hold a trunk call (either incoming or outgoing) while making a local call, it will be access;

21 first assumed that station #30 is connected in a trunk call over trunk line #I in the manner ex plained in detail in the section titled. Outgoing trunk calls. The distant-exchange person is ad'- vised by the person at station #30 to wait on the line for a few moments. The person at. station #30 then depresses the commontrunk-line holding key into the operated position where it locks, this action connecting ground to the lower winding of relay I60 in trunk line #1 by Way Qf'contact 543 and Working spring of station #30 lineswitch, contact 5 of common trunk-line holding key, conductor 582; bank contact 552 and conductor I62, and also unlocking trunk-line #I' conn ng key. Trunk-l #I conne tin key restores to the normal position. The connecting of ground to the lower winding of relay 160 shunts out this winding and causes relay ISO to operate on its upper winding over the circuit from ground, contact 543 and working spring of station #30 lineswitch, contact 5!! of common trunk-line holding key, direct-current loop through telephone 5Ill, conductor 58'I, bank contact 550 conductor I6I, upper winding of relay 16!],resting contact of armature. I32, conductor 'IOI to negative battery at the distant exchange.

At armature I6 I, relay I60 completes the circuit to relay I50 over an obvious circuit, causing relay I5Il to operate and lock to ground byway of contacts MI and I52. At armature I53, relay 150 bridges the windings oi relay 160' across the trunk circuit to the distant exchange in order to retain the holding and supervisory conditions unchanged at the distant exchange. At armature I, relay I50 completes the circuit to relay 130, causing relay I to operate. At armatures 732 and I34 and respective working contacts, relay 130 replaces the holding bridge previously connected across the trunk circuit at armature I53- with the winding of relay- I40, thereby maintaining the holding and supervisory conditions unchanged at the distant exchange; The relay I60 holding bridge is opened at the resting contacts of armatures I32 and 134. Armatures 132 and 134 are fitted with contacts of the make-beforebreak type to insure continuity of the holding bridge across the trunk circuit.

The returning of trunk-line #I connecting key at station #30 telephone to normal position by the operation of the common trunk-line holding key opens the circuit to pull-down magnet 540 at contact SM, and the plunger of station #30 lineswitch is withdrawn from the bank trunk connected to trunk line l. The bank contacts 550 55 I 552 and 553 are opened by the withdrawal of station #30' lineswitch plunger, and the plunger is automatically aligned with the shaft of the master switch. The opening of bank contact 553 opens the circuit to relay Hi1, and relay I'IO restores. At armature I14 and resting contact, relay I18 extends trunk start conductor I83 to trunk start relay 'I'8ll, thereby making trunk line #I- accessible to all, local stations associated with trunk start conductor I83. At armature I35 and working contact, relay I30 extends trunk start conductor i61- to trunk start re lay 180, thereby making trunk line #I- accessible to all local stations associated with trunk start conductor I61. The restoration of armature 54I by the release of pull-down magnet 54!] opens an additional point in the circuit of pull-down magnet 540 at the working spring of contact 543: at contact 543 and resting spring, connects ground to line conductor 582 of station #30; and, at contact 544, connects line relay 520' of station #30 lineswitch to line conductor 5'81.

The restoration of relay Till occurs before-relay 740 operates from the distant-exchange loop, nd relay Hil co q y, lo k o ro nd by way of armature 134i and working contact, armature TN and armature, its before its operating circuit is-opened at armature 'i5l. Relay 'l3Ilis of the slowrto release type toinsure continuity of operation. At armature 73L relay 539 mmpletesthe circuit to trunk line lcall-held signal, or signals, to inform the local stations thata dis.- taint-exchange connection is being held on trunk line #I.

After the. person at station #30 has operated the. common trunk-line holding key to connect a holdin bridge across trunk line #1, he next depresses thev local-call connecting key into the operated position where it looks. The line relay 52B of station #39 lineswitch, tens relay 230, units relay 2 It and localstart relay 358 (assuming that local link #i has been ire-assigned) operate to causethe master switch to align the plunger of station #36 lineswitch with the bank trunk leading tothe answering end of local link #l in the manner. described in detail in the section titled Local calls. Pull-down magnet 54s is then automatically operated to cause the plunger of station #33 lineswitch to plunge into the bank trunk leading to. the answering end of local link #1:, thusconnecting station #39 telephone with line relay 4&5 of link #i. The person at station #Bil, upon receiving dial tone, dials the number of the desired local station, and the connection between the two local stations is completed in the manner described in the section titled Local calls.

The person at station #35! may return to the held; distant-exchange connection on trunk line #i, or the person at the called local station may accept the held trunk connection. In either case, access to trunk line #i is obtained by'depressing trunk-line #i connecting key at. the local station,

and the plunger of the local-station lineswitch is caused to plunge into the bank trunk leading to trunk line #I in the mannerpreviously described in the section titled Outgoing trunk calls. Ground on conductor Its then causes relay llll in trunk #I tooperate, and at armaturel'll relay 'Illl' opens the locking circuit to relay J30. The restoration of relay. its removes the winding of relay I49 from across the trunk. circuit at. the working contacts of armatures T32 and 735i, causing relay Mil to restore; and, at the resting contacts-of armatures $812 and E34, re-connects trunk conductors "Hi! and ill-2 to the windings of relay 160. The talking circuit is now complete between the local station and the distant exchange over trunk line #i'. At armature l3l,'relay I30 opens the circuit to trunkeline #l call-held signal, or signals. At armature it' l and working contact, relay Till switches trunk start conductor EB-3 to conductor I84, thus making trunk line busy to calls from other local stations associated with trunk start conductor 183. At armature I35 and resting contact, relay 7313 switches start conductor It! to conductor I64 by way of armature H3 and resting contact, making trunk line busy to calls from other local stations associated with. start conductor lei.

Busy over-ride on trunk calls As previously explained in the section titled Incoming trunk calls, trunk start relay J of trunk line #I is normally connected te -trunk start conductor 783 through the resting contact of armature I'M. Consequently, when trunk line #1- is taken into use, trunk start relay 780 is disconnected at the resting contact of armature I'M by the operation of relay T over conductor I63 and, therefore, no idle local station associated with trunk start conductor I83 can have access to busy trunk line #I. Similarly, trunk start relay 180 is disconnected from trunk start conductor I61 at the working contacts of armatures H3 and 135 and, hence, no idle local station associated with trunk start conductor I61 can have access to-busy trunk line #I. Trunk start relay 180, however, is directly connected to trunk start conductor I68 without contact intervention and, consequently, any local station associated with trunk start conductor [68 has access to trunk line #I regardless of whether trunk line #i is in use or not.

It is thus apparent that station #20, for example, automatically over-rides the busy guard condition on an established trunk connection between the distant exchange and another local station when the handset piece at station #20 is lifted and the related trunk-line connecting key is depressed. This busy over-ride feature enables the person at station #20 to exercise a supervisory control over trunk calls involving other local stations, and to obtain a trunk line when all the trunk lines are in use by requesting the persons on a particular trunk connection to relinquish the trunk line.

Conference service on trunk calls The busy over-ride feature described in the preceding section titled Busy over-ride on trunk calls enables a conference call to be held on a trunk connection by two or more local stations. Such local stations are associated with trunk start conductor H38 in the manner shown in Fig. 1 for station #20.

Now, when one of the local stations associated with trunk start conductor 168 has connected with trunk line #I, for example, and then desires to have another local station join in the conversation, a holding bridge is connected across trunk conductors llll and 102, in the manner described in detail in the section titled Holding and transferring trunk calls. Next, the second local station is called over a local interconnecting link, in the manner described in the section titled Local calls, and is instructed to connect with trunk line #I. Since both the calling and called local stations are associated with trunk start conductor I68, it is inconsequential which station connects with trunk line #I first, as both stations automatically over-ride the busy condition when the respective trunk-line #l keys are depressed. Transmission battery is supplied to the local stations over the trunk line from the distant exchange, and the permissive number of local stations on the trunk line is governed by the desired quality of transmission.

Having described the invention and what is considered new and desired to be protected by Letters Patent is set forth in the following claims:

1. In a telephone system, subscribers lines each having two connect keys, individual lineswitches terminating said subscribers lines, two groups of trunks accessible to said lineswitches, a master switch for directing said lineswitches, means controllable over a calling subscribers line responsive to the actuation of one of the two keys of said celling line for operating said master switch to position the lineswitch of said calling line in alignment with a trunk of one of said groups and then automatically cause said lineswitch to seize said one trunk, said means also controllable over said calling line responsive to the actuation oi the other key of said calling line for operating said master switch toposition the lineswitch of said calling line in alignment with a trunk line of said other group and then automatically cause said lineswitch to seize said one trunk of said other group.

2. In a telephone system, an exchange,'subscribers stations therein each having a connect key, lineswitches associated with said stations, a pro-selected link accessible to said lineswitches for extending connections from said stations, control equipment including directive switching mechanism for causing the lineswitch of a calling station to seize said pro-selected link said control equipment controlled by the operation oi said key at said calling station.

3. In a telephone system wherein lineswitches terminate subscribers stations, at least two con nect keys'at each of said stations, trunk lines accessible to said lineswitches in common, the number of said trunk lines equalling the number of said connect keys at each of said stations, each said trunk line associated with one of said connect keys at each of said stations, a master switch for controlling said lineswitches, means responsive to the actuation of one of said connect keys at one of said stations for operating said master switch to cause the lineswitch of said one station to connect with the trunk line associated with said operated connect key.

4. In a telephone system wherein lineswitches terminate subscribers stations in a local exchange, a local link accessible to said lineswitches for extending local connections from said stations, a distant exchange, trunks accessible to said lineswitches for extending trunk connections from said stations to said distant exchange, a lo-- cal connect key and trunk connect keys at each of said stations, the number of said trunk keys at each of said stations equalling the number of said trunks, each said trunk key at each of said stations fixedly related to a designated one of said trunks, a master switch, means including said master switch responsive to the operation of said local key at a calling station for causing the lineswitch of said calling station to seize said local link, means including said master switch controlled by said calling station over said seized local link for causing the lineswitch of a desired.

called station to seize said local link, means for completing a talking connection between said calling and called stations over said seized local link, and means including said master switch responsive to the operation of a trunk key at a second calling station for causing the lineswitch of said second calling station to seize the trunk related to said operated trunk connect key.

5. In a telephone system, a plurality of subscribers lines each having a key, a plurality of trunk lines accessible to said subscribers lines, a common directive switching mechanism, means responsive to the actuation of the key of a calling subscribers line for operating said mechanism to cause the connection of said calling line with one of said trunk lines, means for freeing said mechanism and rendering it available for subsequent use in response to the connection of said one subscribers line with said one trunk line, and means thereafter controlled by the calling subsoriber over said one trunk line for operating said mechanism to cause a desired called subscribers line to also connect with said one trunk line. 

